Fans of Harry Potter no doubt dream of having their very own invisibility cloak, and so-called “metamaterials” could one day make that dream a reality.
And now it appears that these same materials could also bring scientists one step closer to a longstanding fantasy of Star Trek fans: warp drive.
A paper was published recently on the arXiv by a University of Maryland physicist named Igor Smolyaninov suggesting the properties a metamaterial would need to possess in order to simulate the effects warp drive would have on the path of light.
Metamaterials are special because they have been specifically engineered to exhibit unusual properties, particularly with regard to how light behaves when it passes through such materials. For instance, scientists have created metamaterials with a negative index of refraction (known as “left-handed materials”).
The effect is a bit like dropping a pebble in a calm body of water and having the ripples spread inward, rather than outward. That property could potentially reflect light in such a way to make ordinary objects invisible to the naked eye, or to “cloak” objects from radar.
There’s something else that can manipulate light: gravity. Einstein’s theory of general relativity describes how spacetime can curve in response to mass — and the more massive said object, the more radically spacetime could curve. Light, in turn, will follow that curvature. This offers some tantalizing possibilities for exotic phenomena, from black holes to wormholes and, yes, warp drives.
Back in 1994, a physicist named Michael Alcubierre famously proposed a way to build a warp drive despite the proscription against faster-than-light travel imposed by relativity. He envisioned a scenario in which, rather than having the space craft move, it is encased within a bubble of spacetime that shrinks in the direction you wish to travel, while stretching out behind you. And the spacecraft moves with the bubble.
However, even Alcubierre admitted that such a bubble of spacetime would be extremely unstable, and thus faster-than-light travel remains out of reach.
It’s still an interesting theory, and numerous computer simulations have been devised to test various aspects of Alcubierre’s work. It would be even better to construct tabletop experiments, which is where metamaterials come in. They can provide a means of simulating how light would behave under extreme gravitational conditions.
Baylor University’s Richard Obousy emphasizes that Smolyaninov’s findings are not an exact duplication of how light would behave under warp drive conditions, merely “a simulation of the path a light ray would travel” in response to such conditions. He compares it to using a prism or mirror to refract or reflect light along specific paths.
“The prism or mirror is not actually bending spacetime, it is merely mimicking the effect,” he told Discovery News. “Analogously, metamaterials provide experimentalists the ability to mimic, or simulate exotic light ray trajectories thanks to the remarkable property negative refraction.”
What Smolyaninov has done, says Obousy, is “derive some of the features that a metamaterial would need in order to simulate the Alcubierre warp drive in the lab.” According to Smolyaninov, if it is indeed possible for such bubbles to form in spacetime, it should also be possible to simulate these bubbles inside a metamaterial — although so far, his calculations indicate that there is no metamaterial scientists could physically build in the lab that would allow for faster-than-light travel.
Right now, his best simulations reach about 25% the speed of light — and since it’s a simulation, there’s no actual propulsion taking place.
That’s still an impressive velocity to achieve, even in a simulation. And given the rapid progress to date in new kinds of metamaterials, who knows what new properties scientists will be able to engineer in the coming years? Says Obousy, “Although Smolyaninov’s paper won’t directly assist us in getting to Alpha Centauri, it is certainly a welcome tool for physicists interested in exploring some of the properties of warp drives in the lab.”
